Projection display systems have improved dramatically over the last decade. The color gamut and purity has improved at the same time remarkable improvements in resolution and image brightness have also been made. On top of these changes, the size, weight, and cost of the projectors have fallen dramatically. These improvements have led to entirely new markets for the projectors. For example, mobile professionals are now able to carry their own projectors to presentations to ensure compatibility between their portable computer and the display projector. These portable computers weigh less than three pounds, yet produce excellent images even in relatively bright environments.
In spite of the very small size and weight of the state of the art projectors, consumers desire even smaller and lighter projectors. Producing further reductions in size and weight have been challenging. The optical components are difficult to shrink. Of special concern is the arc lamp. The arc lamp is comprised of two electrodes in a glass ampoule. This glass ample contains a gas that is heated to a plasma by the arcing between the electrodes. A reflector collects the light from the plasma and focuses the light into the aperture of the illumination optics of the display.
Explosion is a common failure mode of arc lamps. The force of the explosion is quite strong, and the glass shards created by the explosion must be contained within the projector. Without containment, the glass shards easily can damage optical components in the projector or become lodged in the other electrical and mechanical components. The glass shards must also be prevented from exiting the projector case. A glass plate, thick enough to stop the glass shards created by the explosion of the lamp, typically is placed over the end of the reflector to contain the explosion. Unfortunately, this glass plate interferes with the air flow intended to cool the arc lamp.
The arc lamp creates a tremendous amount of heat, much of it in long wave infrared energy. The infrared energy cannot pass through the glass plate and creates an unfavorable thermal environment for the arc lamp. Specifically, the excess temperature leads to oxidation of the electrodes and devitrification of the lamp wall materials. Thus, the excess heat reduces the life of the arc lamp. One way to reduce the heat is to enlarge the size of the reflector to increase the space between the arc and the reflector wall. Unfortunately, enlarging the reflector limits how small the projector can be. What is needed is a method of cooling the burner that does not enlarge the size of the projector.